The present invention relates to a hydraulic control circuit system for controlling two double-acting hydraulic cylinders individually or collectively at the same time.
The invention can be applied to a front loader or the like to control a hydraulic cylinder associated with the loader arm to lift and lower the latter and a second hydraulic cylinder used for turning a working implement, such as a bucket, pivotally connected to the free end of said arm. Therefore, the invention will be described by way of example as applied to a front loader but, of course, it is not limited thereto.
A loader, such as a front loader, has a bucket, fork, blade or other attachment pivotally connected to the free end of its arm which is swingable in a vertical plane, and includes individual hydraulic cylinders for operating said arm and said attachment. Conventionally, these hydraulic cylinders have been individually or independently operated by multi-position directional control valves. Therefore, if the arm alone were lifted or lowered with the bucket filled with the load, the bucket would tilt with respect to the horizontal and the load would spill. It is necessary, therefore, to turn also the bucket in operative association with the upward and downward movements of the arm so as to maintain the bucket horizontal. However, the conventional manner of individually manipulating the respective operating levers of the two directional control valves so as to effect satisfactory operation of the two cylinders is inefficient and liable to cause mistakes in operation. Additionally, it is often necessary to maneuver the tractor at the same time. Thus, a number of operations must be performed at the same time. Therefore, such inefficient manner of operation greately lowers the efficiency of operation.
The dump action of the bucket should advantageously be as rapid as possible in order to provide increased efficiency of operation and improved release from the bucket of its relatively adhesive contents, such as earth and sand, livestock feedstuffs, and snow. To this end, various proposals have been made, including one for increasing the size of hydraulic pumps and pipings, one for using a vacuum prevention valve to rapidly project the rod under the weight of the load and its own weight, and one for arranging a directional control valve in the form of a differential circuit. These proposals, however, have disadvantages in cost, operation and back pressure rise due to pipings and valves and have not been satisfactory. On the other hand, in the case of relatively easily crushable farm products, such as beets, potatoes and cabbages, it is desirable to discharge them relatively slowly so as to avoid damage thereto. Therefore, it is desirable that any suitable value for the rotative speed of the attachment, namely, for the rod advancing or projecting speed of the dump cylinder associated therewith be selectable in accordance with the type of the object to be handled.
Further, the conventional front loader has been provided with either a single-acting or a double-acting lift cylinder for lifting and lowering the arm, but both cylinders have their merits and demerits from the standpoint of function, often causing much inconvenience to the operator depending upon working conditions. Therefore, it is desirable for a single front loader to have both functions from the standpoint of efficiency of operation and rate of operation.